Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
A spindle motor rotates the disk (or disks) at a high speed so that the head essentially flies over the disk surface on an air bearing. When the disk drive is powered on, a spin-up operation is executed in order to spin up the disk to the operating speed before loading the head over the disk surface. It is desirable to spin up the disk as fast as possible in order to minimize the delay before a host may access the disk drive. In addition, it may be desirable to achieve a substantially consistent spin-up time across a family of disk drives so that a disk drive manufacturer may provide an accurate specification for the spin-up time, thereby enabling the design of storage systems based on the spin-up specification.